Figure 1. Role of helper T cells in priming of tumor specific effector T cells.
Step 1. Vaccination with helper peptides allows antigen presenting cells (APCs) to take up tumor specific helper peptides in addition to tumor antigen directly from dying tumor cells. Step 2). APCs migrate to the lymph node where they interact with CD4 T cells through MHC class II molecules. Step 3). CD40 on the CD4 T cells ligates CD40L to mature the APC, which leads to enhanced MHC class I expression as well as costimulatory molecules CD70 and CCL3 and CCL4. Step 4) The chemokines recruit CD8 T cells to the complex, and binding the MHC molecules with costimulation induces optimal effector priming. The primed effectors proliferate and are capable of trafficking to the tumor site.